Acyloxysilanes are functional chemicals which are used as reagents for precise synthesis and synthetic intermediates in pharmaceuticals, agricultural chemicals, electronic materials and the like, as well as raw materials for surface modifiers, sol/gel materials, nanomaterials, organic and inorganic hybrid materials, and the like.
As general methods for producing an acyloxysilane, the following methods are known, for example: (A) a method in which a chlorosilane is allowed to react with a carboxylic acid directly or in the presence of a base (Patent Documents 1 and 2); (B) a method in which a chlorosilane is allowed to react with a metal carboxylate (Patent Document 3); (C) a method in which an acyloxysilane is allowed to react with a carboxylic acid (Patent Document 4); (D) a method in which a hydrosilane is allowed to react with a carboxylic acid in the presence of a transition metal catalyst (Patent Document 5); (E) a method in which a chlorosilane is allowed to react with a carboxylic anhydride (Patent Document 6); (F) a method in which silanol is allowed to react with a carboxylic anhydride (Non-patent Document 1); and (G) a method in which an alkoxysilane is allowed to react with a carboxylic anhydride (Non-patent Document 2).
However, the methods using a chlorosilane are associated with the following problems: (1) handling of raw materials is not easy, since a chlorosilane, which generates corrosive hydrogen chloride due to hydrolysis, is used (methods A and B); (2) corrosive hydrogen chloride is produced as a byproduct, in cases where a base is not used in the reaction with a carboxylic acid (method A); (3) a large amount of salt is produced as a byproduct, in cases where a base is used in the reaction with a carboxylic acid (method A); (4) a large amount of salt is produced as a byproduct, also in the reaction with a metal carboxylate (method B); (5) an acyl chloride, which is susceptible to hydrolysis and prone to generate corrosive hydrogen chloride, is produced as a byproduct, in the reaction with a carboxylic anhydride (method E); and the like. Further, the method using an acyloxysilane, a hydrosilane, or silanol (method C, D or F) is associated with a problem that such a silicon compound or the like is not necessarily easily available, is expensive, or the like. In addition, the method using an alkoxysilane (method G) has a problem that a mixture of raw materials needs to be heated at a high reflux temperature for a prolonged period of time, and thus, a more industrially advantageous approach has been demanded.
On the other hand, regarding the applications of acyloxysilanes or related silicon compounds, a method has been known, as one of the methods for carrying out a surface treatment of a solid material, in which a trialkoxysilane such as triethoxysilane or trimethoxysilane, or triacetoxysilane or the like having a higher reactivity, is used as a so-called silane coupling agent (Non-patent Document 3).
However, the method using a trialkoxysilane has the following problems: the operational process is not simple, since a trialkoxysilane is less likely to react directly with the surface of a solid material, and thus it is necessary, in general, to convert it into the structure of silanol by carrying out the hydrolysis of alkoxy groups in the presence of water; the efficiency of the surface treatment is not necessarily high, because a coupling reaction of silanols simultaneously proceeds along with the reaction with the solid material surface; and the like. In contrast, the method using triacetoxysilane is associated with problems such as, for example, that easily obtainable, commercially available types of triacetoxysilane are limited to specific types. The reason for this is as follows: although triacetoxysilane has a high reactivity with a solid material surface, the use thereof in a conventional method results in an increased production cost; triacetoxysilane is unstable to moisture or water, and has a low storage stability; or the like.